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Potosí is a city and the capital of the department of Potosí in Bolivia. It is one of the highest cities in the world by elevation at a nominal 〔(Bolivia & Main Cities / Potosí ) from boliviaweb.com. Retrieved 2010-09-27.〕 For centuries, it was the location of the Spanish colonial mint. Potosí lies at the foot of the ''Cerro de Potosí''〔Not to be mistaken with Cerro Potosí, Mexico〕—sometimes referred to as the ''Cerro Rico'' ("rich mountain")—a mountain popularly conceived of as being "made of" silver ore, dominates the city. The Cerro Rico is the reason for Potosí's historical importance, since it was the major supply of silver for Spain during the period of the New World Spanish Empire. The silver was taken by llama and mule train to the Pacific coast, shipped north to Panama City, carried by mule train across the isthmus of Panama to Nombre de Dios or Portobelo whence it was taken to Spain on the Spanish treasure fleets. Cerro de Potosí's peak is above sea level.〔 ==Geology== Located in the Bolivian Tin Belt, Cerro Rico de Potosi is the world's largest silver deposit and has been mined since the sixteenth century, producing up to 60,000 tonnes by 1996, and estimates are that much silver still remains. Potosi became the second largest city, and the site of the first mint, in the Americas. By 1891, low silver prices prompted the change to mining tin, which continued until 1985. At peak production in the sixteenth and seventeenth centuries, the ore contained up to 40% silver.〔Cunningham, C.G., Zartman, R.E., McKee, E.H., Rye, R.O., Naeser, C.W., Sanjines V., O., Ericksen, G.E., Tavera V., F., 1996, The age and thermal history of Cerro rico de Potosi, Bolivia, Mineralium Deposita, 31, 374-385〕 The ore deposits reside in veins present in the dacite volcanic dome. The hill is "honeycombed" with underground workings, reaching from the summit to depths of . The conical hill has a reddish-brown gossan cap of iron-oxides and quartz, with grayish-blue altered dacite and many mine dumps below.〔 Basement rocks consist of Ordovician clastic sediments consisting of phyllite with some sandstone interbedding. At about 13.8 Ma, the dome was extruded. During the explosive process, the Venus breccia formed when the ascending dacite magma reacted with groundwater to produce a phreatic eruption. The released pressure allowed the formation of the Caracoles tuff ring on top of the breccia. The magma then extruded outward from a dike to form a volcanic dome over the tuff. The dacite dome is by at the surface and narrows down to the wide dike at depth. Hydrothermal circulation and fracturing soon followed, altering the dacite and depositing ore minerals and gangue in the veins.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Potosí」の詳細全文を読む スポンサード リンク
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